Funds are requested for an ACAS 570 Interactive Laser Cytometer from Meridian Instruments. This instrument is unique and not available at our institution. It has several major capabilities not available with other cytometers. One is the ability to analyze the fluorescence emission of suitably-stained individual cells in monolayer culture, which we will utilize for analysis of immunofluorescence, calcium, pH, and S-phase DNA content. All users have applications involving anchorage-dependent cells. Another unique capability is the ability to measure fluorescence recovery after photobleaching (FRAP), which we will use for analysis of membrane lateral motion dynamics, and communication via gap junctions. A third feature is digitized image analysis which will be used for localization of immunofluorescence and membrane probes. The rapid high-- resolution confocal imaging capability, which we require, is unique. The major user group constitutes 16 biomedical research programs, all supported by the National Institutes of Health, which will account for 95% of usage. Limited access to the instrument will be available to other investigators through members of the major user group. The research areas involved deal with membrane dynamics in several cell systems, membrane formation in nerve cells, membrane mitogens and control of neuronal cell proliferation, transmembrane signaling, mechanisms of neuronal excitability, lipid metabolism in liver and testis cells, control of DNA synthesis, immunotoxicology of chemical xenobiotics, factors affecting the immune system in an animal model for AIDS and ion transport in renal cells.